Side chains vs Tree chains. An explanation by Peter Todd

I think the most basic explanation of the difference is that in side-chains you put your trust in miners - if at any point there is a miner with enough hashing power to 51% attack the side-chain they can destroy it instantly, and often steal all the funds associated with it too. Now if a majority of all miners agree to mine your side-chain that may be ok and you won't be attacked, but getting to that point essentially requires asking permission from those miners if you want your side-chain to exist at all. With tree-chains we create a global, yet scalable, blockchain publishing service that everyone contributes to and everyone uses. Everyone works together to keep that layer secure, and anyone can write code to make use of it. The disadvantage is that you can't rely on miners to verify for you - you have to verify blocks client-side - but that also means those same miners ...